The impact of environmental change and human land use on alluvial valleys in the Loess Plateau of China during the Middle Holocene

In recent years a growing number of studies have reported proxy evidence for Holocene climatic and environmental change on the Loess Plateau of north-central China. Pollen from lake cores and sediment analyses from loess sections firmly point to a warm-moist Mid-Holocene Climatic Optimum. Archaeological evidence indicates that at the same time, human agricultural settlements expanded into this area during the Middle Neolithic Period. A geoarchaeological study of sediment sections from several valleys within the catchment of the Yiluo River, Henan Province, indicates a sequence beginning with a stable landscape, soil development and high water tables in the Early Mid-Holocene, which was exploited by Early Neolithic millet farmers in the Peiligang Period. Subsequently, there was a rapid shift to episodes of hillslope erosion and increased valley alluviation in the later Mid-Holocene. The resulting alluvial sediments, dating from 5300/5010 cal. BC through 2130/1870 cal. BC, represent clay-rich water-logged deposits that contain sediment and phytolith evidence for the first rice paddy farming in this region. This coincides with the first migration of Neolithic rice farmers to the area in the Yangshao Period ca. 5500 cal. BC. These fills, temporally and stratigraphically linked to archaeological sites and human land-use practices, suggest that they originated as a direct result of human impact on the landscape. After ca. 2000 cal. BC, Holocene valley incision in this catchment led to narrowing floodplains, the disappearance of the valley wetland deposits, and a reduction in land available for paddy farming.